High molecular weight polyesters and particularly linear polyesters derived from 1,4-cyclohexanedimethanol have been available for a number of years. These are described inter alia in Kilber et al, U.S. Pat. No. 2,901,466. This patent discloses that the polyesters are particularly advantageous as film and fiber-formers. The compositions disclosed herein are also used for injection molding, extrusion and other plastic forming operations.
Recently, it has been suggested to incorporate a brominated epoxy resin as a flame retardant for polybutylene terephthalate molding compositions. A useful brominated epoxy resin is one formed by reacting tetra-bromobisphenol-A and epichlorohydrin. This is exemplified in U.S. Pat. No. 3,965,212 wherein tetrabromobisphenol-A, optionally non-brominated bis-phenol-A and epichlorohydrin are reacted to form a glycidyl ether-endcapped brominated resin useful as a flame retardant for polybutylene terephthalate. A flame retardant synergist such as antimony trioxide is also added. The epoxy resins which are disclosed in U.S. Pat. No. 3,965,212 however, are of relatively low molecular weight having at most about 11 repeating units of the bisphenol-A-containing ether. Other patents which teach improving the flame resistance of polybutylene terephthalate with the brominated epoxy resins described above together with other brominated aromatic compounds include U.S. Pat. Nos. 3,909,485; 4,548,964; and 4,562,216.
It has been found that many of the aforementioned brominated flame retardants have the drawback that when the same are added to polybutylene terephthalate and the mixture subjected to molding, the resulting molded articles are greatly deteriorated in mechanical properties, particularly toughness.
It has now been unexpectedly discovered that reinforced mixtures of a polyester resin derived from a cyclohexane dimethanol and a carbocylic dicarboxylic acid or ester, and a tetra brominated bisphenol-A epoxy oligomer endcapped with epichlorohydrin as a primary flame retardant unexpectedly exhibit an improvement in certain mechanical properties while showing an improvement in thermal stability.